1. Field of the Invention
The invention relates to a lifting vehicle having a holding and lifting device for holding and lifting or lowering goods.
Lifting vehicles of this type are in use in many embodiments. Lifting vehicles of this type designed in the manner of a forklift truck have a driver""s position with a central operating device, from which the vehicle is driven and the handling of the transported goods is controlled. In this case, in front of the driver""s position there is a vertical guide in the form of a mast or the like, on which a holding device is guided such that it can be moved vertically. The holding device can be constructed as a gripping device in order to transport particular goods.
2. Background Description
Using such a lifting vehicle, goods which are firstly heavy and secondly sensitive are often transported, such as paper reels in a print shop. The paper reels set down on an end are in this case gripped by a tongs-like gripper, are lifted and, for the purpose of transport, are rotated into a horizontal position of the cylinder axis of the paper reel. At the destination, the gripping device is rotated through 90xc2x0 again in order to set the paper reel down again at one end. This setting down requires particular care, since in the event of not precisely vertical lowering of the end of the paper reel, the sections of the windings of the paper reel which contact the floor first are pressed in because of the high pressure, so that the unwound paper web is no longer smooth at the edge in the desired manner and is therefore unusable for many applications. In serious cases, a complete paper reel which, to an order of magnitude, weighs some tons, can become unusable. This applies similarly when the action of setting the paper reel down on the floor is not carried out at the necessary slow speed and the end of the paper reel is compressed highly on the floor. In this case, too, the paper at the edge of the paper reel becomes unusable.
The same is of course true for other sensitive goods which are transported by a lifting vehicle. The operator of a lifting vehicle therefore bears a considerable responsibility for the proper handling of goods which, under certain circumstances, may be valuable. In some cases, it is therefore expedient to be able to establish when damage to valuable goods has occurred during transport.
WO 79/00330 has disclosed a lifting vehicle with the features mentioned at the beginning, the sensor arrangement being formed, for example, by a potentiometer, with which the relative inclination of the lifting forks in relation to a reference plane, for example the supporting plane for the wheels of the lifting vehicle, can be indicated. In order to pick up the goods, in this case the holding forks can be brought into a horizontal position. An upward inclination prevents the goods picked up slipping off the forks, while a downward inclination is used for unloading. In the case of a gripping device for gripping paper reels, a precise vertical position ensures that the clamping arms run parallel to the axis of the paper reel.
The present invention is based on the problem of constructing the lifting vehicle in such a way that the operator can be supported or monitored better and more comprehensively by monitors during the proper handling of the goods transported by the lifting vehicle.
Starting from this problem, according to the invention a lifting vehicle of the type mentioned at the beginning is defined by the fact that the sensor device has at least one acceleration measuring device for determining the instantaneous inclination and/or the instantaneous acceleration of the holding device.
The lifting vehicle according to the invention therefore has an acceleration measuring device with which the instantaneous inclination and/or the instantaneous acceleration of the holding device can be determined. The acceleration measuring device can also detect static accelerations, so that the acceleration due to gravityxe2x80x94and therefore the inclination relative to the verticalxe2x80x94is measured.
If the holding device can be rotated about only one axis of rotation, which for example is at right angles to the guide of the lifting device, only one inclination measurement in a plane parallel to the guide is also practical, since any inclinations as a deviation from a desired position can be compensated for only in this plane as a result of the rotation of the holding device. However, if there is also a further possible adjustment, for example by means of pivoting the guide of the lifting device, it is practical for the sensor device to be designed to detect the instantaneous inclination in three-dimensional space. To this end, the sensor device can have two acceleration measuring devices substantially orthogonal to each other.
It is possible to imagine equipping the sensor device in such a way that it outputs an optical signal, for example, when an inclination of the goods which is not beneficial to setting them down is detected. However, preference is given to a connection between the sensor device and the operating device, so that for example the operating device can be equipped with an indicator for the instantaneous inclination of the holding device. Additionally or alternatively, it is possible to provide a processing stage in the operating device, which uses the output signals from the sensor device to influence the control of the holding and lifting device, specifically in such a way that, for example, only inclination-free setting down of the goods on the floor of a hall or a rack shelf is possible.
In a particularly preferred embodiment of the invention, the sensor device is connected to the operating device via a wire-free transmission link, for example via radio.
In order to indicate the measured inclination, the evaluation device must have information about the zero position. The zero position can be xe2x80x9clearnedxe2x80x9d from a plurality of measurements, so that evaluation with an appropriately programmed microcomputer is possible. However, it is also possible to determine the zero position by means of a reference value, which is generated by a second sensor device for setting up a reference value for the instantaneous inclination of the chassis of the vehicle. This arrangement is expedient if the floor on which, for example, a paper reel is to be set down and on which the lifting vehicle is traveling itself has an inclination. In this case, the alignment of the paper reel only to the vertical would have the effect that the end of the paper reel would be set down obliquely relative to the floor, which according to the invention is to be avoided. In this case, a correction can be made via the measured inclination of the chassis. The second sensor device can expediently be arranged in the operating device itself, so that transmission of the data from the second sensor device to the operating device can be dispensed with.
Since a plurality of lifting vehicles are often moved in a store, it is expedient to provide transmitter-receiver encoding for the wire-free transmission from the sensor device to the operating device, so that a receiver can be programmed to a specific transmitter.
The normal acceleration measuring devices suitable as inclination sensors exhibit a certain temperature sensitivity. It can therefore be expedient to pick up the respective operating temperature in the region of the sensor device with a temperature sensor and to perform compensation for the temperature drift via a characteristic curve recorded previously. In this way, it is possible to carry out the inclination measurement reliably for a range of use from xe2x88x9240xc2x0 C. to +80xc2x0 C.
The sensor device according to the invention can be constructed in such a way that, if appropriate, in addition to the inclination measurement, the determination of the instantaneous accelerations in three-dimensional space is also possible. These signals can expediently be stored in a memory device, in order to be able to determine when the sensitive goods have been exposed to an acceleration which has or could have led to damage to the sensitive goods during transport. In a similar way, the recording of the inclinations may also be expedient for transported goods which are sensitive to inclination.
The second sensor device provided according to the invention can, in an alternative embodiment or else in addition to the second sensor device fitted to the vehicle, be arranged on a set-down surface, on which the goods held by the holding device are to be set down. As a result, differences between the inclination of the travel path of the lifting vehicle, on the one hand, and the set-down surface, on the other hand, can be taken into account, so that even in these cases sensitive goods can be set down exactly perpendicular to the set-down surface, without damage.
The second sensor arrangement is expediently connected to the operating device via a wire-free transmission link.
The output signals from the first sensor device and from the second sensor device are therefore available in the operating device. In a preferred embodiment, difference signals are formed in the operating device and can possibly be used as an indicator for the driver of the lifting vehicle, but preferably used directly to control the holding and lifting device, in order to bring the difference signal to zero when setting down on the set-down surface.